Photo and photo-oxidative degradation of two poly(p-phenylene vinylene) (PPV) derivatives have been examined under nitrogen and air environment, respectively. PPV derivatives based on a single phenyl ring and a biphenyl ring in the backbone structure were used to aid the interpretation of the photo and photo-oxidative reactions. Chemical structural changes were studied using Fourier transform infrared spectroscopy. The evolutions of various aromatic carbonyl functional groups were identical in both PPV derivatives. The mechanism of photo and photo-oxidative degradation is similar in both PPV derivatives. However, the different backbone structure was found to affect the rate of photo and photo-oxidation.